According to the National Institutes of Health, obesity is one of the most daunting health challenges of the 21st century. Approximately 2/3 of all adults are overweight or obese. Efforts to abate the growing prevalence of obesity have not been successful. The Strategic Plan for NIH Obesity Research proposes preventing and treating obesity through lifestyle modification. The purpose of this study is to evaluate the effectiveness of a theory-based intervention framed within the Health Promotion Model (HPM) in facilitating weight loss and maintenance through promotion of healthy eating and physical activity among an underserved, vulnerable population of overweight or obese rural women aged 50-69. During these years, women experience increases in peri- and post-menopausal health risks that are magnified if they are overweight or obese. Weight loss will reduce risks and enhance functional status as they age. Maintenance of weight loss will be emphasized. The Internet offers a way to reach isolated rural women who have limited options for weight loss guidance. A convenience sample of 306 rural women age 50-69 with body mass index 28 to 39.9 will be randomized into 3 groups. All participants will access a theory-based interactive Internet site based on constructs in the HPM and addressing recommended approaches to healthy eating and physical activity for weight loss and maintenance. One group will use the Internet site only, a second group will participate in a supplemental peer-led online support group, and a third group will receive supplemental professional weight loss counseling via e-mail. This study will have 3 phases: guided initial weight loss (6 months), guided continuing weight loss/maintenance (12 months) and self-directed weight maintenance (12 months); the 30-month period will allow time for women to establish lifestyle changes to achieve weight maintenance. The maintenance phases will provide a transition to a permanent healthy lifestyle during the time of high risk for regain. The primary outcomes will be change in body weight, eating, and activity at 3, 6, 12, 18, 24, & 30 months. At least 5% and preferably 10% of loss of weight without regain will be the realistic targets emphasized in this study. Change in behavior-specific cognitive/ perceptual influences from the HPM also will be examined to validate the theory base for the intervention. If successful, this research study will have implications beyond Nebraska for reaching rural populations through the Internet for weight loss and maintenance.